Smart homes are increasing these days which are equipped with many electrically controlled moving parts. For example, such smart homes are typically equipped with an electric lock mounted to the entrance door to allow the entrance door to be locked and unlocked without using a key. It is required that an electric key mounted to an entrance door be not only electrically locked and unlocked, but manually locked and unlocked using a conventional key in case of an emergency such as a power outage.
JP Patent 4847266 discloses one of electric locks which can be locked and unlocked both electrically and manually. The electric lock disclosed in JP Patent 4847266 includes clutch gear driven by a motor, and three clutch members (a first clutch piece, a second clutch piece, and a locking piece) mounted inside the clutch gear and rotatably fitted on a fixed clutch shaft while being superimposed on each other in the axial direction. When an electric driving force is applied, the clutch gear and the clutch members become locked together, and the clutch members engage a drive arm, so that the drive arm drives a dead bolt through a manually driven input member (tumbler) to which a manual force is applied from a key or a thumb turn, thereby locking or unlocking the electric lock. When a manual driving force is applied, the clutch gear and the clutch members are unlocked from each other by the drive arm, which is operatively coupled to the manually driven input member, and simultaneously, the manually driven input member drives the dead bolt, thus locking or unlocking the electric lock.
Of the three clutch members of the electric lock disclosed in JP Patent 4847266, the second clutch piece is a fan-shaped member having engaged portions at the circumferential ends thereof which is configured to engage one end of the drive arm. Wedge-shaped spaces are defined between the outer peripheral surface of the second clutch piece and the inner peripheral surface of the clutch gear, and a roller is received in each wedge-shaped space so that when the roller in at least one of the wedge-shaped spaces is wedged into a narrow portion the wedge-shaped space, the clutch gear and the second clutch piece become locked together.
Since the second clutch piece is a fan-shaped member, the rollers, through which the clutch gear and the second clutch piece are locked together, cannot be arranged at uniform intervals over the entire circumference of the clutch gear. Their number is small, too, compared with the number of rollers arranged uniformly over the entire circumference (only two rollers are used in the embodiment, of which one slips when the other locks up).
Thus, when the clutch gear and the second clutch piece become locked together, high surface pressures are applied from the rollers. This could result in premature wear of the inner peripheral surface of the clutch gear and the outer peripheral surface of the second clutch piece during use of the electric lock, i.e., deformation of the wedge-shaped spaces, to such an extent that the clutch gear and the second clutch piece cannot be properly locked together, thereby making it impossible to electrically lock and unlock the electric lock. While the clutch gear and the second clutch piece are locked together, the roller that is wedged into a narrow portion of the wedge-shaped space presses the second clutch piece against the clutch shaft, causing the second clutch piece to rotate while in sliding contact with the clutch shaft, so that the rotation torque of the second clutch piece could increase to such an extent that the electric lock cannot be electrically locked and unlocked smoothly. Also, driving torque tends to fluctuate due to uneven wear of the outer peripheral surface of the clutch shaft and the inner peripheral surface of the clutch shaft fitting hole of the second clutch piece, and/or due to decentering of the clutch shaft.